The present invention relates to hermetic coatings for multichip modules and polymer film structures.
In one form of high density interconnect (HDI) circuit module, an adhesive-coated polymer film overlay having via openings covers a substrate which can support integrated circuit chips in chip wells. The polymer film provides an insulated layer upon which is deposited a metallization pattern for interconnection of substrate metallization and/or individual circuit chips through the vias. Methods for performing an HDI process using overlays are further described in Eichelberger et al., U.S. Pat. No. 4,783,695, issued Nov. 8, 1988, and in Eichelberger et al., U.S. Pat. No. 4,933,042, issued Jun. 12, 1990. Generally a plurality of polymer film overlays and metallization patterns are used.
In another form of circuit module fabrication, as described by Cole et al., U.S. Pat. No. 5,527,741, issued Jun. 18, 1996, a method for fabricating a circuit module includes using a flexible interconnect layer having patterned metallization on a base insulative layer and an outer insulative layer. At least one circuit chip having chip pads is attached to the base insulative layer and vias are formed in the outer and base insulative layers to expose selected portions of the base insulative layer metallization and the chip pads. A patterned outer metallization layer is applied over the outer insulative layer extending through selected ones of the vias to interconnect selected ones of the chip pads and selected portions of the base insulative layer metallization.
Modules fabricated using the above processes have improved reliability when effectively sealed. Conventional hermetic sealing teachings include welding, soldering, or glass-sealing a prefabricated hermetic lid to a package including the module. These processes are not conformal to the module and typically result in significant increases in packaging volume. Furthermore, when dielectric materials such as glass or ceramic are used as sealing materials, electrical input/output connections must be formed prior to sealing.
Neugebauer et al., U.S. Pat. No. 5,336,928, issued Aug. 9, 1994, describes a conformal hermetic barrier fabricated by depositing a continuous copper film and subsequently electroplating lead over the copper. The resulting conformal barrier requires a continuous metal layer and a plurality of electrical connections cannot easily be made though the hermetic layer.
Thus there is a particular need for an inexpensive conformal hermetic coating fabrication process having (a) deposition conditions compatible with module materials (preferably at temperatures below 200xc2x0 C.), (b) conformal deposition over non-planar topography; (c) depositions free of pin holes; (d) appropriate dielectric properties; (e) patterning processes and materials compatible with module materials; (f) good adhesion to underlying materials and any subsequentlydeposited materials; (g) resistance to damage from chemical attack or mechanical abrasion; and (h) robustness in the presence of temperature fluctuations. It would further be desirable to form a plurality of electrical connections through the hermetic seal without the loss of hermeticity.
Amorphous hydrogenated carbon films, commonly referred to as diamond like carbon (DLC) films, are used as dielectric materials and as scratch protection coatings for various applications but have not been used to provide hermetic barriers.
In the present invention, DLC is deposited in multiple hard and soft layers to form a composite DLC film possessing hermetic properties.